The present invention relates to a heat-developable recording material, and more particularly to a heat-developable recording material with an excellent stability against fluctuations in heat development conditions.
Methods for forming an image by heat development are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Morgan and B. Shely, Imaging Processes and Materials, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d A, 8th ed., page 2, compiled by Sturge, V. Walworth and A. Shepp, Neblette (1969). The photosensitive material used contains a reducible non-photosensitive silver source (e.g., organic silver salt), a catalytic amount of photocatalyst (e.g., silver halide), and a reducing agent for silver, which are usually dispersed in an organic binder matrix. This photosensitive material is stable at room temperature. While these photosensitive materials are stable at room temperature, they produce blackened silver when heated, after light exposure, to a high temperature (e.g. 80xc2x0 C. or higher) through redox reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. This reaction is promoted by a catalytic action of latent image generated by the exposure. The silver produced by the reaction of the reducible silver salt in the exposed region provides a black image and this presents a contrast to the non-exposed region. Thus, an image is formed.
Thus obtained black image is used in recording materials for microfilm medical use such as Roentogen imaging, and printing plate making. These conventional recording materials are based on a photographic principle, and development thereof generally rely upon methods using process chemical solution. There is, however, an urgent need for addressing environmental issues, so that a heat development system without using such process chemical in a solution form and thus free from environmental impact is desired.
There is also a strong need for reducing waste process solution in the field of photoengraving from the viewpoints of environmental preservation and space saving. Thus desired is a technology related to photosensitive heat-developable material for photoengraving allowing efficient light exposure with a laser scanner or laser image setter, and capable of providing a clear black image with a high resolution and sharpness.
The heat-developable recording material, however, suffers from difficulties in precisely defining the development process conditions as compared with the conventional development method using a processing solution. For example, the photosensitive material is heated for development after light exposure, where non-uniformity in the temperature distribution may result in a large difference in image quality. In particular for photosensitive material for printing plate making, a gradation hardener is used for amplifying information in the exposed area to obtain an ultrahigh contrast image, where a minute retardation of the development process may be output with quite a large difference in the density of the black image produced by silver. To suppress such difference in the image quality depending on the developing conditions, it is thus desired to provide a technology for efficiently accelerating the development only at the exposed region. When viewed from another aspect, such acceleration effect of the development will also shorten the developing time, and may be advantageous in rapid image creation.
Approaches for creating an ultrahigh contrast image appropriate to printing plate making based on so-called dry silver process are known in the literatures below. U.S. Pat. Nos. 5,464,738 and 5,512,411 disclose the use of sulfonyl hydrazine compounds as a reducing agent. U.S. Pat. Nos. 5,496,695 and 5,536,622 disclose the use of hindered phenol compounds as a reducing agent, along with the use of a certain kind of hydrazine compounds as an ultrahigh contrast agent. U.S. Pat. No. 5,545,515 discloses the use of hindered phenol compounds as a reducing agent and acrylonitrile compounds as an ultrahigh contrast agent. Problems to be overcome, however, still remain even with these compounds since higher temperature or longer time period is necessary for the development.
A reducing agent for the dry silver has already been known, which can be found in, for example, JP-A-7-13295 (the code xe2x80x9cJP-A-xe2x80x9d as used in this specification means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), JP-A-7-5621, U.S. Pat. Nos. 3,667,958 and 5,350,669. In these patents reported are examples of combined uses of, for example, polyhydroxybenzenes and hydroxylamines. It is, however, still difficult with these techniques to satisfy the performance desired at present.
It has been reported to use, as a reducing agent, phenol compounds having as a substituent an amino group substituted by an electron withdrawing group (e.g. sulfonamidophenol). For example, independent uses of sulfonamidophenol compounds, such as 2,6-dichloro-4-benzenesulfonamidophenol and p-benzenesulfonamidophenol, as a reducing agent are known by JP-A-49-80386, JP-A-5-257227 and JP-A-10-221806. These methods are, however, disadvantageously slow in development speed so that degradation of the image quality due to such delay in the development is inevitable. These methods are also unfavorable in terms of increasing trends in fogging.
Several accelerating techniques have already been known, which are disclosed in, for example, U.S. Pat. No. 5,637,449, No. 5,545,505, No. 5,545,507 and No. 5,496,695. A satisfactory level of acceleration effect for the development has, however, not been reached, and the problem in the degradation of image quality due to delayed development still remains unchanged.
It is therefore an object of the present invention to solve the conventional technology described above. That is, a problem to be solved by the present invention relates to provision of a heat-developable recording material with a small sensitivity changes against fluctuations in heat development conditions, thereby to allow stable heat development.
The present inventors found out, after extensive studies, that stable image formation was achieved even under fluctuated heat development conditions by using a compound having a specific structure, which has led us to the present invention.
That is, the present invention provides a heat-developable recording material having, at least on one side and the same side of the support, (a) reducible silver salt, (b) a reducing agent other than a compound represented by the general formula (1) below, (c) a binder, and (d) at least one compound represented by the general formula (1) below; content of the compound represented by the general formula (1) being 0.01 to 100 mol % with respect to the reducing agent: 
[where in the general formula (1), R1, R2, R3, X1 and X2 independently represent a hydrogen atom; halogen atom; or substituent which is bound to the benzene ring via a carbon atom, oxygen atom, nitrogen atom, sulfur atom or phosphorus atom. At least either X1 or X2 represents a group represented as xe2x80x94NR4R5, where R4 and R5 independently represent a group selected from a hydrogen atom, alkyl group, alkenyl group, alkynyl group, aryl group, or a group represented by xe2x80x94C-(xe2x95x90O)-R, xe2x80x94C-(xe2x95x90O)-C(xe2x95x90O)-R, xe2x80x94SO2-R or xe2x80x94SOxe2x80x94R. R represents a group selected from a hydrogen atom, alkyl group, aryl group, heterocyclic group, amino group, alkoxy group and aryloxy group. Adjacent groups of the above substituents may bind each other to form a ring.]
In a preferred embodiment of the present invention, the heat-developable recording material is a heat-developable photosensitive recording material containing a photosensitive silver halide, and preferably using hindered phenol compounds as a reducing agent.
It is also preferable to use an ultrahigh contrast agent in the present invention. Preferable ultrahigh contrast agent can be at least one compound selected from the group consisting of the compounds respectively represented by the general formulae (2), (3) and (4), below: 
[where in the general formula (2), R6, R7 and R8 independently represent a hydrogen atom or substituent, and Z represents an electron withdrawing group or silyl group. In the general formula (2), R6 and Z; R7 and R8; R6 and R7; or R8 and Z may bind with each other to form a ring structure. In the general formula (3), R9 represents a substituent. In the general formula (4), X and Y independently represent a hydrogen atom or substituent; and A and B independently represent an alkoxy group, alkylthio group, alkylamino group, aryloxy group, arylthio group, anilino group, heterocyclic oxy group, heterocyclic thio group or heterocyclic amino group. In the general formula (4), X and Y; or A and B may bind with each other to form a ring structure.]
According to the present invention, a heat-developable ultrahigh contrast photosensitive material suitable for printing plate making is obtained in which a high sensitivity and small difference of sensitivity under fluctuated conditions in heat development are attained while keeping a sufficiently small Dmin, and in which, in particular for the case of combined use with an ultrahigh contrast agent, an ultrahigh contrast, high Dmax, small difference of sensitivity under fluctuated conditions in heat development and high process stability are attained while keeping a sufficiently small Dmin.